This invention relates generally to radio frequency (RF) antennas, and more particularly to RF array antennas.
As is known in the art, a radar or communications system antenna generally includes a feed circuit and at least one conductive member generally referred to as a reflector or radiator. As is also known, an array antenna includes a plurality of antenna elements disposed in an array in a manner wherein the RF signals emanating from each of the plurality of antenna elements combine with constructive interference in a desired direction.
In commercial applications, it is often desirable to integrate RF antenna arrays into the outer surfaces or xe2x80x9cskinsxe2x80x9d of aircraft, cars, boats, commercial and residential structures and into wireless LAN applications inside buildings. It is desirable to use antennas or radiators which have a low profile and a wide bandwidth frequency response for these and other applications.
In radar applications, it is typically desirable to use an antenna having a wide frequency bandwidth. A conventional low profile, wideband radiator has been a stacked-patch antenna which includes two metallic patches, tuned to resonate at slightly different frequencies and supported by dielectric substrates. Thicker substrates (e.g., foams) are preferred in order to increase bandwidth, but there is a trade-off between bandwidth and the amount of power lost to surface waves trapped between the substrates. This trade-off places a restriction on the scan volume and overall efficiency of the phased arrays. Additionally, thick foams increase volume and weight, and absorb moisture which increases signal loss.
Surface waves produced in stacked-patch radiators have undesirable effects. Currents on a patch are induced due to the radiated space waves and surface waves from nearby patches. Scan blindness (meaning loss of signal) can occur at angles in phased arrays where surface waves modify the array impedance such that little or no power is radiated. The array field-of-view is often limited by the angle at which scan blindness occurs due to surface waves.
Waveguide radiators used in xe2x80x9cbrickxe2x80x9d type phased array arrangements (i.e. the feed circuit and electronics for each antenna element is assembled in a plane perpendicular to the antenna radiating surface) do not suffer from internal surface wave excitation with scan angles which limits scan volume, but these waveguide radiators typically do not have a low profile or a wide bandwidth. In addition, individual waveguide radiators must be fabricated and assembled in a brick type architecture thus increasing costs and reducing reliability.
It would, therefore, be desirable to provide a low cost, low profile radiator with a wide bandwidth and a large scan volume which can be used with tile-based or brick-based array arrangements which can be used in land, sea, space or airborne platforms applications.
It is an object of the present invention to provide a low cost, wide bandwidth, linear or circularly polarized waveguide radiator in a tile array arrangement, meaning all feed networks and active electronics are stacked vertically within the unit cell boundary for each antenna element, without the undesirable surface wave effects normally found in stacked patch antennas.
It is a further object to provide a radiator which can assume arbitrary lattice arrangements such as rectangular, square, equilateral or isosceles triangular, and spiral configurations.
In accordance with the present invention, a radiator includes a waveguide having an aperture and a patch antenna disposed in the aperture and electromagnetically coupled to the waveguide. With such an arrangement, each radiating element and associated feed network are electro-magnetically isolated from a neighboring radiating element, thus eliminating internal surface wave excitation and therefore extending the conical scan volume beyond xc2x170xc2x0.
In accordance with another aspect of the present invention, an antenna includes an array of waveguide antenna elements, each element having a cavity, and an array of patch antenna elements including an upper patch element and a lower patch element disposed in said cavity. Such an arrangement provides a low cost, wide bandwidth, linear or circularly polarized waveguide radiator in a tile array arrangement, which in one embodiment includes feed networks and active electronics stacked vertically within the unit cell boundary for each antenna element.
In accordance with another aspect of the present invention, an antenna includes a first dielectric layer having a first plurality of patch antenna elements responsive to radio frequency signals having a first frequency, a first monolithic conductive lattice disposed adjacent to said first dielectric layer, a second dielectric layer comprising a second plurality of patch antenna elements responsive to radio frequency signals having a second different frequency, disposed adjacent to said first monolithic conductive lattice. A second monolithic conductive lattice is disposed adjacent to said second dielectric layer, and the first lattice and said second lattice form a plurality of waveguides, each waveguide associated with each of a corresponding first and second plurality of patch antenna elements. Such an arrangement provides a radiator which can assume arbitrary lattice arrangements such as rectangular, square, equilateral or isosceles triangular, and spiral configurations and a wide bandwidth, low-profile, slot-coupled radiator having the bandwidth of a stacked-patch radiator and the large scan volume of a waveguide radiator.